1. Field of the Invention
The invention relates to a bituminous binder emulsion with a viscosity controlled by addition of scleroglucan.
2. Related Art
The use of emulsions of bituminous binders in road construction and repair, for the surfacing of roadways, soil stabilisation, sealing in civil engineering or in buildings or similar applications is well known. The emulsions which are suitable for these applications are generally of the "oil-in-water" type and consist of a dispersion of an organic phase made up of fine globules of the bituminous binder in a continuous aqueous phase, the said aqueous phase containing an emulsifying system which promotes the dispersion of the globules of the bituminous binder in the aqueous phase and consists of one or more emulsifying agents and optionally a pH regulating agent which, depending on the case may be an acid, a water-soluble salt or a base. Such emulsions are usually classified according to the nature of the emulsifying system employed to ensure the dispersion of the bituminous binder in the aqueous phase and according to whether the said emulsifying system consists of one or more anionic, cationic, nonionic or amphoteric emulsifying agents, the corresponding emulsions will be known as anionic, cationic, nonionic or amphoteric respectively.
The emulsion of a bituminous binder is considered to be a means which makes it possible to lower the viscosity of the said binder during the operations making use of this binder. After breaking, the emulsion restores the bituminous binder to which the emulsifying system and other additives which are present in the aqueous phase have been added. The emulsion of bituminous binder behaves like a liquid at room temperature and in the production of surface dressings it is commonplace to incorporate a thickening agent in the aqueous phase of the emulsion, whose function is to increase the viscosity of the emulsion to be spread on the support to be treated so as to keep the emulsion in place on the support and thus, to ensure, before gravel is applied, a uniform distribution of this emulsion on the said support, whatever the slope of the support. Thus, references FR-A-2,577,545 and FR-A-2,577,546 describe cationic emulsions of bituminous binders into which there may be incorporated a thickening agent consisting, for example, of a water-soluble natural resin such as guar gum, gum arabic, ghatti gum, karaya gum, tragacanth gum, locustbean gum, xanthan gum or else of a water-soluble polyurethane of low molecular mass and especially a polyurethane of viscometric molecular mass of less than 20,000, which results from the action of one or more polyisocyanates with one or more polyols chosen from polyesterpolyols and polyetherpolyols.
The use of conventional thickening agents such as those mentioned above for controlling the viscosity of the emulsions of bituminous binders may result, particularly when the bituminous binder is a bitumen/polymer binder, in breaking of the emulsion which takes place in two stages, namely a first stage of rapid breaking of a part of the emulsion, followed by a second stage of slower breaking of the part of the emulsion which did not break in the first stage, the result being, apart from a long total period of breaking, that a broken bituminous binder is obtained which is not very cohesive and is consequently not highly elastic.